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Old 21st November 2013, 01:25 AM   #1
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Default Why are external amplifiers superior?

Whether you're on a tablet or smart phone, you probably know how poor the audio quality is. Use an external amplifier & you're more than likely to notice a difference.

But why?


A colleague of mine mentioned he wanted to pick up a new set of head phones. I recommended that he look into an external amplifer. Like most people, he told me he didn't need it that loud.

sigh.

How can I explain that the benefit of an external amplifier isn't just limited to increasing the volume (I'm being vague here!).

Let's call my colleague Tim. If Tim listens to his Ipod at half volume, & the music isn't distorting, then why would he need an external amplifier?

Perhaps the absolute moment you turn up the volume knob, the sine wave begins to clip (even though you can't tell ...yet). I thought that the sine wave didn't begin to clip UNTIL it started squaring off.


I'm just not getting it. I can play a song at X volume using just my Ipod & it will sound OKAY. I can play that same song at that same X volume using my Ipod AND an external amplifier & it will sound better (at least I hope so)

If niether signal has began to clip, then why would the external amplifier sound better? There must be more to this than just the sine wave, no?

It's sloppy, but I hope this works!
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Old 21st November 2013, 12:37 PM   #2
00940 is offline 00940  Belgium
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There might be a few reasons:

- the internal amplifier has increasing distortion as the load is more difficult to drive (decreasing in resistance). Not uncommon. An external amp will present an input impedance of 10k to 100k, to be compared to the 16 to 300r of headphones.
- the internal amplifier has a highish output impedance while the external amp has a low output impedance. This will affect the frequency response of some headphones.
- the external amp has higher distortion but with a "nicer" sounding spectrum. Masking effect at work.
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Old 21st November 2013, 12:45 PM   #3
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External amplifiers cost more and are less convenient, so they must sound better.
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Old 21st November 2013, 01:04 PM   #4
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Generally the built in amplifier is built to a budget and a size. Quality is not the most important factor.

The small size means that compromises have to be taken both in layout and component choice.

As soon as these limitations are removed there will undoubtedly be an increase in quality.
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Old 21st November 2013, 01:18 PM   #5
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I'm not debating that. The subtlety is that if you plug an external amplifier into the headphone jack, the sound has to pass through the bad amplifier before it can even get to the good one.
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Old 21st November 2013, 01:21 PM   #6
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Quote:
Originally Posted by TylerTraulich View Post
Whether you're on a tablet or smart phone, you probably know how poor the audio quality is. Use an external amplifier & you're more than likely to notice a difference.
This does not need to be true at all!

It all depends on the headphone impedance and output impedance of the smart phone/tablet. If the headphone impedance is 8x higher or more then you will not notice any frequency deviations.
Loudness levels depend on headphone sensitivity and voltage output of the smart phone/tablet.

NwAvGuy has made a good article about it: NwAvGuy: Headphone Amps/DACs Explained

And of cause Scopeboy said it already: External amplifiers cost more and are less convenient, so they must sound better. The placebo effect and conformation bias are strong factors in these things
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Old 21st November 2013, 01:50 PM   #7
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Quote:
Originally Posted by scopeboy View Post
External amplifiers cost more and are less convenient, so they must sound better.
yep

Add that to the top of my list.
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Old 21st November 2013, 06:22 PM   #8
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Quote:
Originally Posted by scopeboy View Post
I'm not debating that. The subtlety is that if you plug an external amplifier into the headphone jack, the sound has to pass through the bad amplifier before it can even get to the good one.
I think you missed the part where it was pointed out that an external amplifier represents a much easier load to the "bad" amplifier, thus greatly reducing distortion. Also the explanation of the differing output impedances- built in amplifier usually has a higher output impedance compared to an external amplifier. All this makes a world of difference in the distortion profile.

Battery operated devices have amplifiers where the primary design parameter is low power consumption. Cellphones have nasty, nasty class D amplifiers. I don't know what's inside an ipod, but I doubt that it's optimized for audio.

I used to think that the headphone output of my old CD player (RIP it's an audio amplifier now ) was pretty good until I prototyped a headphone amp that used 4 5532s in parallel. This is far from optimal, but it's so much better than what you will find in virtually all commercial designs. Headphones are an afterthought in most designs.

Here we design and build class A headphone amps that are optimized in every way for their intended use. Sure you can buy them on fleabay and amazon etc, but they are "boutique" items and you pay way too much. With DIY and a hundred dollars, the sky's the limit.
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Old 21st November 2013, 10:40 PM   #9
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Quote:
Originally Posted by Fast Eddie D View Post
I don't know what's inside an ipod, but I doubt that it's optimized for audio.


... and care to explain what's so bad about class D?
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Old 21st November 2013, 10:47 PM   #10
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In my experience, amplifier sound is mostly about the power supply. Decent power supplies are bulky, no way around that that I know of. No room in a smartphone for anything approaching a decent PSU. When the PSU's suboptimal, as Fast Eddie says the lighter the load, the better the SQ. But I reckon its not 'lower distortion' that makes the SQ difference, its lower PSU noise. Offload the load to the external amp (don't choose one without a reasonably bulky PSU, meaning plenty of caps called for) and you're closer to audio nirvana

@xnor - what's so bad about classD is the PSU noise tends to be worse than for classAB. ClassA's reputation is built on lowest PSU noise.
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Last edited by abraxalito; 21st November 2013 at 10:50 PM.
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